The present invention relates to a multi-gradation liquid crystal display device which is capable of freely switching between a standard definition image display and a double definition image display. The invention also pertains to a method for driving such a multi-gradation liquid crystal display device.
Conventionally, a multi-gradation liquid crystal display device includes drivers for driving column lines (also referred to as source or data lines) and row lines (also referred to as gate lines) arranged in a two-dimensional matrix form in a display panel. An electric signal corresponding to image data of one row line is set in the source driver for driving the column lines. The row lines are selectively driven by the gate driver, while at the same time the above-mentioned electric signal is provided via the column lines from the source driver to all picture elements (each of which is a smallest display unit defined by one of display electrodes arranged in a matrix form on the display panel) connected to a selected one of the row lines; thus, gradation data is written. This operation is repeated for each of the row lines which are selected in a sequential order.
Generally, analog image data is transferred to the source driver of the multi-gradation liquid crystal display device and stored in its memory after voltage level conversion and rearrangement for picture elements. All pieces of the image data for all picture elements to be connected to a selected one of row lines, thus set in the memory of the source driver, are simultaneously provided therefrom onto the column lines, and in synchronism with this, the row line concerned is selectively driven by the gate driver. During this period all pieces of image data for all picture elements to be connected to the next row line are transferred to and stored in another memory of the source driver from the outside. Upon completion of the outputting the image data to the column lines and upon completion of the selective driving of the row line concerned, the next line is selected and all the corresponding pieces of image data stored in the memory are provided onto the column lines. These operations are repeated for each of the uppermost to the lowermost row lines of the two-dimensional matrix in the display panel to provide thereon a display.
Alternatively, analog image data or the like from a computer or similar source, for example, is once converted to digital image data, which is subjected to various image processing and then converted to analog form for sequential input into a memory in the source driver. Thereafter, the analog image data is provided to all picture elements connected to one row line by the operation of the source driver and the gate driver in the same manner as mentioned above, and a display is produced by the repetition of such operations.
In the two-dimensional matrix form of arrangement of the row and column lines in the multi-gradation liquid crystal display panel, picture elements are arranged in various forms. In the case of a monochrome display, picture elements A.sub.2m(i-1)+1 to A.sub.2mi corresponding to each row line i (i=1, 2, . . . , 2 n) are all connected thereto as shown in FIG. 1A. In the case where red (R), green (G) and blue (B) picture elements constituting each color pixel C for a color display are arranged, for instance, in a delta form, the R, G and B picture elements are selectively connected to two gate lines as shown in FIG. 1B. In the case where the R, G and B picture elements forming each color pixel C are arranged in a stripe form, they are connected to one row line as shown in FIG. 1C. In these cases, the driving method by the gate driver differs according to the manner of data storage in the source driver and its output to the column lines. The prior art therefore requires, for a double definition display and for a standard definition display, different display panels having different numbers of column and row lines and different source and gate drivers.
Incidentally, technology of this kind is introduced in "Handbook on Liquid Crystal Devices" Nikkan Kogyo Shimbunsha, 1980, in which a drive and write system for liquid crystal displays is described at pages 387 to 466 and a color display system for liquid crystal displays at 467 to 523.
As mentioned above, the prior art needs different liquid crystal display panels dedicated to a double definition display and a standard definition display, respectively. Further, since input image signals handled in such display panels differ in signal rate, the source and gate drivers differ in operating speed with panels accordingly, and the prior art has dealt with this problem by changing their constructions or by employing different drivers. Since these drivers drive large numbers of column and row lines in the panel, dedicated multi-output ICs with many drive terminals have been developed, and as the source driver, various ICs have also been developed which perform digital image signal processing or analog image signal processing, depending on whether the display to be provided is a monochrome, multicolor or full-color display. However, such ICs are used equivocally in accordance with the definition of the liquid crystal display panel and the color to be displayed, and the same display panel and the same circuit construction are not used in common to the double definition display and the standard definition display, for example, but instead different kinds of display panels and drivers are prepared and selectively used for each particular display.